<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="./lib/vue-2.4.0.js"></script>
</head>
<body>
    <div id="app">
        <!-- 监听文本框数据的改变 -->
        <input type="text" v-model="firstname"> +
        <input type="text" v-model="lastname">
        <input type="text" v-model="fullname">
    </div>

    <script>
        var vm = new Vue({
            el : "#app",
            data : {
                firstname : "",
                lastname : "",
                fullname : ""
            },
            methods: {
            },
            watch:{ // 监视 data 中指定数据的变化，然后触发watch中对应的 function 处理函数
                firstname : function(newVal, oldVal){
                    //this.fullname = this.firstname + "-" + this.lastname
                    this.fullname = newVal + "-" + this.lastname

                },
                lastname : function(newVal){
                    this.fullname = this.firstname + "-" + newVal
                }
            }
        })
    </script>
</body>
</html>